Characterization of the chemical transition across the extratropical tropopause using AIRS data

The chemical transition between stratosphere and troposphere is controlled by both dynamics and chemistry. Characterizing the transition on a global scale is a critical step for identifying the relevant tropopause definitions for stratosphere troposphere exchange calculations. We present a diagnosis of chemical transition across the extratropical tropopause on a global scale using AIRS data. In particular, we use the tracer relationships from AIRS measurements of ozone and water vapor across the extratropical tropopause to examine the mixing between stratosphere and troposphere and to characterize the chemical transition in relation to the thermal and the dynamical tropopause. The initial results confirm the previous analyses using aircraft data that the chemical transition is better located using the thermal tropopause instead of a specific potential vorticity surface. The dynamical tropopause using PV gradients is also investigated. We show that the tracer relationships provide an effective tool to diagnose the irreversible exchange between stratosphere and troposphere on a global scale. In addition, we have applied this method to evaluate how well the global models represent this transition across the extratropical tropopause compared to the observations. The performance of NCAR MOZART3 and WACCM models will be discussed.